Pancreatic cancer is known to be one of the most life-threatening cancers characterized by aggressive local invasion and distant metastasis. The high basal level of autophagy in pancreatic cancer may be responsible for the low chemotherapeutic drug response rate and poor disease prognosis. However, the clinical application of autophagy inhibitors was unsatisfactory due to their toxicity and minimal single-agent anticancer efficacy. Hence, oncologists begin to consider the tumor microenvironment when exploring new drug targets. In the present study, the anti-tumorigenic mechanisms of two major phytochemicals derived from Chinese medicinal herbs had been investigated against pancreatic cancer development. Calycosin is a bioactive isoflavonoid of the medicinal plant Astragalus membranaceus. Our results have shown that calycosin inhibited the growth of various pancreatic cancer cells both in vitro and in vivo by inducing cell cycle arrest and apoptosis. Alternatively, calycosin also facilitated MIA PaCa-2 pancreatic cancer cell migration in vitro and increased the expression of epithelial-mesenchymal transition (EMT) biomarkers in vivo. Further mechanistic study suggests that induction of the Raf/MEK/ERK pathway and facilitated polarization of M2 tumor-associated macrophage in the tumor microenvironment both contribute to the pro-metastatic potential of calycosin in pancreatic cancer. These events appear to be associated with calycosin-evoked activation of TGF-β signaling, which may explain the paradoxical drug actions due to the dual roles of TGF-β as both tumor suppressor and tumor promoter in pancreatic cancer development under different conditions. Isoliquiritigenin (ISL) is a chalcone obtained from the medicinal plant Glycyrrhiza glabra, which can be a precursor for chemical conversion to form calycosin. Results have shown that ISL decreased the growth and EMT of pancreatic cancer cells in vitro, probably due to modulation of autophagy. ISL-induced inhibition of autophagy subsequently promoted reactive oxygen species (ROS) production, leading to induction of apoptosis in pancreatic cancer cells. Such phenomenon also contributed to the synergistic growth-inhibitory effect in combined treatment with the orthodox chemotherapeutic drug 5-fluorouracil. In addition, ISL-induced tumor growth inhibition in vivo was further demonstrated in a tumor xenograft mice model of pancreatic cancer. ISL promoted apoptosis and inhibited autophagy in the tumor tissues. Study on immune cells indicates that ISL could reduce the number of myeloid-derived suppressor cells (MDSCs) both in tumor tissue and in peripheral blood, while CD4+ and CD8+ T cells were increased correspondingly. In vitro test has revealed that ISL inhibited the polarization of M2 macrophage along with its inhibition of autophagy in M2 macrophage. These immunomodulating effects of ISL had reversed the pro-invasive role of M2 macrophage in pancreatic cancer.In conclusion, calycosin acts as a "double-edged sword" on the growth and metastasis of pancreatic cancer, which may be related to the dual roles of TGF-β and its influence on the tumor microenvironment. Alternatively, ISL consistently inhibited the growth and metastatic drive of pancreatic cancer through regulation of autophagy and reprogramming of the immune system. The differential modes of action of these compounds have provided new insights in the development of effective pancreatic cancer treatment adjuvants.

Introduction: Dark spots appearing on the skin caused by hyperpigmentation results from the action of tyrosinase, an enzyme whose activity leads to the production of the skin pigment melanin. Extracts of the plant Glycyrrhiza glabra, also known as liquorice, are commonly used to treat a range of conditions including skin hyperpigmentation. This study aimed at isolating and identifying compounds in extracts from South African liquorice root and assaying these compounds as to their antioxidant activity, their ability to inhibit the tyrosinase enzyme and their level of cytotoxicity. Methods: The ability of plant extracts to scavenge free radicals was tested using the 2,2-diphenyl-1-picrylhydrazyl (DPPH), [2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonicacid)] (ABTS) and the ferric ion reducing power (FRAP) tests. The polyphenolic content of extract fractions was determined and extract compounds were identified using UHPLC-QToF-20 MS. In vitro anti-tyrosinase activity was also investigated as well as cytotoxicity in HepG2 liver and SK-MEL-1 melanoma cells using the MTT cell viability assay. Results: Of the four fractions prepared from the 70% methanolic extract of liquorice root, fraction 3 (F3) showed increased polyphenolic content and antioxidant properties with IC50 of 56.1 ± 6.32, 39.14 ± 1.1 and 66.34 ± 1.4 μg/ml against DPPH, ABTS and FRAP, respectively. The anti-tyrosinase activity of this fraction showed an IC50 of 358.54 μg/ml compared to Kojic acid (0.75 mM) used as the control. In addition, this fraction showed reduced liver toxicity as a higher percentage cell viability was noted in the HepG2 cells compared to the SK-MEL-1 skin melanoma cells. However, both cell types showed higher percentage viability compared to acetaminophen that was used as cytotoxic control. The LC-MS analysis revealed the presence of a wide variety of compounds including 4-azido-3-benzyl-coumarin, ferulic acid, glycyrrhizin, quercitrin, cirsilineol, gentioflavine and 4'',6,7-trihydroxyisoflavone. The literature indicates the use of these compounds regarding antioxidant and anti-tyrosinase activity. Significantly, cularidine was identified in this study, a compound not previously reported in studies involving liquorice root. Conclusion: The results from this study concur with previous reports as to the anti-tyrosinase and antioxidant activities associated with liquorice roots, activities perhaps due to the relatively high polyphenolic content in extracts from South African liquorice root. / Life and Consumer Sciences / M. Sc. (Life Sciences)